LGC program requirements and mission constraints on alternate mission AS-278B

Following our AS-206 spacecraft computer program status review at MIT on October 6th, we launched into a discussion of the AS-278B mission and its demands on the guidance system. This alternate mission, you recall, is one in which the LM and command module are launched separately followed by a CSM active rendezvous. The LM would then be manned and a number of spacecraft systems tests would be carried out, perhaps including a LM active station keeping exercise and docking. This would be followed by an unmanned sequence of LM maneuvers basically the same as currently planned for the primary AS-206 mission.

After considerable discussion to establish what seemed to us to be reasonable mission constraints, we arrived at the following list of programs needed to augment the AS-206 program for use on the AS-278B mission. You will note that all of the changes are associated solely with the function of determining the orientation of the platform or aligning it prior to the AS-206 maneuver sequence.

  1. Platform orientation determination is required and maybe a platform alignment program is also required, although we don’t think so.

  2. Star catalogue and associated data handling routines must be added.

  3. Modifications to the routine providing pilot interface with the computer, i.e., input and displays will probably be required.

  4. Preparation of an addendum to the GSOP would be needed and it is to be emphasized that this work would be applicable to the AS-278B mission only.

The following routines were also considered but are apparently not needed for the reasons listed.

  1. G&N power-on and power-off progams. These programs, which are routinely provided on manned spacecraft to assist the pilot in turning on and off this equipment, are probably not needed since it is thought this process can be carried out manually, and it is strictly a one-time affair; i.e., as far as we could tell it is only necessary to turn on the equipment one time and never to turn it off.

  2. Some thought was given to adding special digital auto pilot modes for RCS translation and rotation using the hand controller. Here again it is MIT’s impression that processors are available in the current AS-206 program which can be utilized in the station keeping and docking exercise.

  3. LGC initialization primarily associated with state vector and clock alignment updating. Apparently is is already possible in the AS-206 program to input these quantities both via uplink and DSKY.

  4. Special programs to initialize and start the AS-206 maneuver sequence. Apparently the present AS-206 program already has these capabilities by means of uplink and DSKY inputs.

As you can see, the list of programs required has really been reduced to a minimum. In addition, these programs are probably required in very nearly the same form for the later missions, which means work on them is not entirely wasted. The list was kept this small by assuming that certain constraints on the mission were acceptable. In large part, this was done by carrying out a number of functions, manually by the crew, which are ordinarily under computer control. This will be apparent by glancing through the following list of constraints which I certainly don’t claim to be complete, and in fact, some of the items listed may not even need to be there.

  1. No provision is made for re-rendezvous in the LGC. In this category, note there is no processing of the LM rendezvous radar by the LGC nor is there attitude control in the LM program for aligning its rendezvous lights toward the CSM.

  2. It is assumed that no change will be required to the AS-206 maneuver sequence program. I would like to point out, however, that considerable flexibility exists in the targeting and timing of the maneuver as the program is presently formulated.

  3. Platform alignment to within about 5° of the preferred orientation about all 3 axes is acceptable for the AS-206 maneuver sequence. The intent here is to provide a coarse alignment of the platform while docked through use of the command module G&N. Of course, it would then be necessary to determine precisely the resulting orientation of the LM platform.

  4. There will be no provision in the LC to assist the astronaut in locating stars in the AOT. This must be done manually with whatever assistance is possible from the CSM.

  5. It is probable the crew must check contents of the erasable memory word by word via the DSKY to insure that all critical parameters are stored properly after the LGC is turned on the first time. I am referring here to quantities such as accelerometer bias: scaling factor, etc., equivalent to those quantities loaded by the K-start tape prior to launch. This is probably not unique to AS-278B.

  6. The only DSKY display programs to be implemented will be associated with the platform orientation determination program and those required for the crew to check out the contents of the erasable memory.

  7. The G&N power-on and power-off sequence will be carried out manually by the crew.

  8. An LMP will be available and in operation.

  9. The RCS will be manually purged and pressurized.

  10. The S&C band will be turned on manually.

  11. The ECS primary water coolant valve will be manually activated.

  12. No C or S band antenna steering will be provided.

  13. No LGC AGS initialization will be provided.

  14. If LM cold soak is required in the docked configuration, the CSM shall do it.

  15. The LM shall always be extracted from the SIVB by the CSM even if LM 1 spacecraft changes are required [I am not certain this is a constraint imposed by the computer program].

  16. The LM will be powered down during launch and until manned [here again I am not certain this is a program constraint]. This implies

    a) There will be no launch T-M

    b) There will be no launch abort or contingency orbit insertion capability.

[If it is determined that the LM can be launched powered-up, I should point out that the AS-206 program does provide these capabilities.]

Of course, the status of the AS-278B alternate mission is still quite confused. As I have indicated previously, it is our intention to do nothing now at MIT in support of this mission except to make sure the programs identified above, currently being prepared for the AS-278 program, are given enough priority to assure their readiness when the decision must be made around the end of November as to what we are going to do. In addition, we will attempt to determine what, if any, impact this activity would have on the AS-278/503 and the AS-504 spacecraft computer program development schedule. I would be very interested to hear from those of you concerned with this matter if you feel that either the list of programs or constraints given above are not accurate or adequate in some way.

Terms & Abbreviations


see AS-207/208


see AS-503


see AS-504


Abort Guidance System.


Alignment Optical Telescope, a "space sextant" the astronauts used to correct the alignment of their intertial guidance system.


Originally scheduled as the first unmanned flight of the LM, it was cancelled after the Apollo 1 fire. The AS-206 launch vehicle, a Saturn 1B, was used to launch Skylab 2 on May 25, 1973.


AS-207/208 (also known as AS-278) was to have been the first test of the LM in Earth orbit. It was also to have be a dual mission with the command and lunar modules launched on separate Saturn 1Bs. The mission was cancelled after the Apollo 1 fire and the Saturn 1Bs were used to launch Skylab 3 (AS-207) on July 28, 1973 and Skylab 4 (AS-208) on November 16, 1978. The LM was first tested by Apollo 5 in January 1968.


see AS-207/208


see AS-207/208


Before the Apollo 1 fire, the mission referred to as AS-503 was an unmanned Earth orbit test flight of the LM and CM scheduled for October 1967. The launch vehicle, SA-503 was used for Apollo 8, December 23 1968.


Before the Apollo 1 fire, the mission referred to as AS-504 was originally scheduled for December 1967. AS-504 eventually launched as Apollo 9, March 3 1969.


Command-Service Module.


The "Display and Keyboard" interface through which the astronauts controlled their guidance computers.


Environmental control system.

Erasable memory

The Apollo Guidance Computer had a small amount of "erasable memory" analogous to the RAM in a modern computer.


Guidance and Navigation.


see Guidance System Operations Plan

Guidance System Operations Plan

The GSOP was essentially the specification for how the guidance computer and its software where required to work for a specific mission. Many of GSOP’s are available online including the GSOP for the cancelled AS-207/208 mission


Lunar Module Guidance Computer.


Lunar Module. Earlier it was known as the Lunar Excursion Module and abbreviated “LEM.” Even after the name change, it continued to be pronounced “lem.”


Lunar Module Mission Programer. A sort of autopilot for operating the LM when it was unmanned. In the end, an LMP was only ever used on Apollo 5. See Apollo experience report: Guidance and control systems; lunar module mission programer


Massachussets Institute of Technology. In these memos, MIT is shorthand for the MIT Instrumentation Laboratory, created and led by avionics pioneer Charles Stark Draper. It is now known as the Charles Stark Draper Laboratory and became independent of MIT in 1973.


Reaction Control System.


The second stage of a Saturn IB or the third stage of a Saturn V.


see S-IVB